1. Field
This disclosure generally relates to an image forming apparatus such as a printer, a facsimile machine, or a copier.
2. Discussion of the Background
A tandem-type image forming apparatus forms a color image to lay a toner image of each color (black, yellow, magenta, and cyan) on the surface of a transfer member. An image-forming unit includes a photoconductive drum, a charge device, a developing device, and a cleaning device. The charge device forms a latent image on a surface of the photoconductive drum charged, which has been uniformly charged. The developing device forms a toner image to develop the latent image. The cleaning device removes untransferred toner on the surface of the photoconductive drum after transferring the toner image to a transfer member.
Japanese Patent No. 4597837 discloses a cleaning device that includes a cleaning brush roller to be rotatable and to contact with a surface of a photoconductive drum and a voltage application member to apply a voltage to a cleaning brush roller for adhering toner electrically. The cleaning brush electrically and mechanically removes the untransferred toner on a surface of the photoconductive drum after transferring the toner image to a transfer member.
A conventional image forming apparatus that includes a power supply unit for each cleaning brush roller of each color (black, yellow, magenta, and cyan) has a high cost and an increased size. Thus, it is necessary to reduce the number of power supply units so that individual power supply units do not apply a bias voltage to each cleaning brush roller.
Further, it is not always necessary to use each colored image-forming unit when using an image forming apparatus included a plurality of image-forming units. Namely, an image forming apparatus can operate in a monochrome mode in which a black toner image is formed using only an image-forming unit for black, and in a color mode in which a color toner image is formed using every image-forming unit.
Therefore, conventionally the power supply unit applies a bias voltage to the cleaning brush rollers of the image-forming units for black as well as yellow, magenta, and cyan, when the image forming apparatus prints a sheet in monochrome mode.
Conventionally, the power supply unit applies power not just to the cleaning brush roller, but also, e.g., to a charge device of the image-forming unit.